Ajapted said:
If dynamicness was required, you would simply not use a BSP tree at all. DukeNukem3D's renderer works fine without one (with map structures isomorphic to Doom's).

Right. A portal engine makes more sense if you want to do stuff like that. I was just thinking about what would be necessary to actually support dynamic BSP, if it were to be implemented for purely academic interest for example.